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Last fall, New York City became one of the few cities in America to implement an energy storage mandate when Mayor Bill Di Blasio announced a 100 MWh by 2020 solar-plus-storage target, but progress has been slow. By the end of 2016, the city had only installed 4.8 MWh of storage.

A new report by the City University of New York, the National Renewable Energy Laboratories and Meister Consultants examines the barriers to deploying solar-plus-storage installations in New York City. The report cites the high cost of battery storage and the lack of city and state incentives for storage. The report also identifies the city’s arduous permitting process as one of the barriers developers face.

But the report does not put a lot of focus on what may be one of the biggest barriers to expanding energy storage in New York: the lack of consensus on fire safety standards for battery storage devices, especially lithium-ion batteries.

Fire safety concerns have not been a limiting factor in other jurisdictions, said Christopher Robinson, who heads energy storage research at Lux Research. But New York City’s population density makes it more of a concern there.

Uncertainty around fire safety issues is putting a damper on the New York storage market, said Davion Hill, energy storage leader, Americas, for DNV GL. “Developers are afraid of the soft costs associated with excessive water and ventilation requirements,” he said.

Unanswered safety questions linger for li-on batteries

The use of li-ion batteries in stationary applications such as businesses or homes is relatively new, new enough that their use leaves unanswered questions among those responsible for public safety.

The two main agencies responsible for the safety of battery storage installations in New York are the Department of Buildings and the Fire Department of New York.

To the FDNY a li-ion battery system is a relatively unknown hazard that raises multiple questions. What type of fire suppressant should be used? What type of emissions does a battery give off? And what is the risk of re-ignition?

Those considerations are addressed in a report released last month written by DNV GL for Consolidated Edison and the New York State Energy Research and Development Authority.

The report treats the hazards associated with battery installations and the mitigation of those hazards at length, but there are a handful of key takeaways. Among the key findings are that water is the most effective cooling extinguisher; the outgassing from a burning li-ion battery is similar to a plastics fire, and thermal runaway can be addressed by cell module design.

The choice of the proper fire suppressant has been one of the biggest challenges in addressing the hazards of battery fires. DNV GL tested the use of aerosols, chemicals and water as suppressants and found that water was the best overall suppressant.

In testing outgassing Hill said DNV GL was surprised to find that the chemical profile of a battery fire closely resembles the emissions of a plastics fire of similar mass.

In terms of battery design, DNV GL recommends that all systems demonstrate that a single cell failure cannot propagate to neighbor cells in a module design, adding that present standards limiting fire from a module may be “adequate, provided external fire ratings and adequate extinguishing metrics are met.”

Two of the report’s key recommendations are for the amount of water needed to extinguish a fire and the ventilation system required to handle outgassing. The DNV GL report proposes 0.1 gallons per minute per kilogram of water as an extinguishing benchmark.

For ventilation, the report proposes a rate of 0.25 air changes per hour (ACH) for most cell failure scenarios with a rate of 10 to 14 ACH for worst case scenarios.

Hill notes that an important aspect of the report’s recommendations is that it does not give static recommendations, such as a kW limit on battery capacity for a space of a given size. “We are looking to give scalable” metrics that would be more useful to developers in a variety of installations, he said.

Hill said he hopes the detailed testing and analysis in his report will be able to move the ball forward. “We are really stuck on the water and ventilation requirements; we need some consensus,” he said.

Hill recognizes the importance of the work – lives are at stake – and that, he said, is why “transparency is so important.”

With the numbers that DNV GL has proposed, Hill hopes to see progress toward the adoption of a fire safety code for residential batteries. “It is time to argue about the numbers,” he said.

Hill hopes that by mid-summer stakeholders will be able to come together and put forward some preliminary code language.

“Instead of competing on the next test, we need to come together and move the ball forward,” he said.